IN THE MONTH OF FEBRUARY, 1842. 181 
represents, pretty accurately, the storm of January 26, 1839, also the great British storm 
of August 17, 1840, and that of January 6, 1839, except that in the south-west quarter of 
the latter, the winds were, perhaps, more south-westerly. 
Diagram No. 4, represents the storm of March 17, 1838, the north-east wind covering 
more than half the region of rain and snow. ‘The storm of December 15, 1839, was 
quite similar to this last, though the north-east wind covered a smaller portion of 
the storm. In some storms there is a predominance of north-east winds; in others of 
the south-east; in some north-west, and others south-west winds; but in all we find 
certain common characteristics, namely, an inward motion, with a tendency to circulate 
against the sun. ‘These are the ordinary features of those storms which are accompanied 
by a gust and sudden oscillation of the barometer. The storm of February 3, 1842, can 
hardly be comprehended under this class. It was so extensive, the motion of the baro- 
meter so slow, and the winds moderate on the second and third, that it seems more pro- 
perly to belong to a distinct class; although on the fourth and fifth, when the winds 
sprung up with some force, we find the characteristics mentioned above. 
Il.. PROGRESS OF THE STORM, 
A second question of some importance is, in what direction and with what velocity 
does the storm advance? It is not difficult to perceive that the general progress of 
storms is eastward, but, when we undertake to assign the direction with minute precision, 
we feel the necessity of a precise definition of the terms “storm,” and the “centre of the 
storm.” I define the centre of a storm to be the point of greatest barometric depression. 
The storm of February 16 travelled, then, from sunrise of the sixteenth to sunrise of the 
seventeenth, five hundred and sixty statute miles in a direction of about north 53° 18’ 
east, although to sunset of the sixteenth, its direction had been about north 74° 46’ east. 
It seems probable that its path was nota straight line, although it is possible that its 
centre, on the morning of the seventeenth, was farther south than I have here assigned, 
there being a deficiency of observations on the southern quarter. Velocity twenty-three 
miles per hour. ‘The storm of February 2 and 3, remained nearly stationary. On the 
fourth and fifth its progress can be pretty accurately traced. It travelled north 62° 17’ east, 
eight hundred and sixty miles in twenty-four hours, or thirty-six miles per hour. The 
direction of the storm of December 20, 1836, cannot be precisely assigned. It was clearly 
eastward, but having only observations from the southern half of the storm, it is impos- 
sible to assign, accurately, the place of greatest barometric depression. 
CONCLUSION, 
The following, then, is my view of the origin of such storms as I have been investi- 
gating. This generalization will probably include the greater part of winter storms, but 
will require some modification when applied to summer storms. Imagine a time per- 
fectly clear, when the wind is from the west, or a few degrees south of west, with the 
barometer and thermometer at their mean heights. This may be regarded as the nor- 
mal state of the atmosphere, and the whole body of air from its upper limit to the surface 
VOL. IX.—49 
